The present invention relates generally to oil pressure transducers used with an internal combustion engine in an automobile, and more particularly, to improvements in a composite cylinder for a mini oil pressure transducer used to measure oil pressure and to produce a corresponding indicator signal.
Modern automobiles typically utilize a fuel injection system for the engine which includes an electric motor to power a fuel pump. In addition to the already described oil pressure indicating function, it is sometimes desirable to incorporate an electrical switch mechanism in an oil pressure transducer to control energization of the fuel pump in response to oil pressure. Specifically, it is desirable to activate the fuel pump motor only after a minimum oil pressure is reached.
A number of United States patents generally disclose a pressure transducer and switch mechanism, either singularly or in combination. For example, U.S. Pat. No. 3,321,594 to Reise, discloses a fluid pressure actuated switch with a diaphragm sensor operatively associated with electrical contacts for controlling an electric fuel pump motor. U.S. Pat. No. 4,255,630 to Hire, also discloses an electrical switch which is responsive to fluid pressure to control a fuel pump motor. U.S. Pat. No. 4,524,255 to Haag, discloses a switch with a movable diaphragm responsive to fluid pressure to open and close contacts of an electrical circuit. U.S. Pat. No. 4,581,941 to Obermann, discloses a fluid pressure transducer including a switch therein, adapted to control a fuel pump motor and utilizes a diaphragm and contacts.
Several other patents have been found which disclose pressure transducers without the switching device. These include U.S. Pat. Nos. 3,504,324; 4,449,112; and 4,452,202. All of the patents discussed or identified previously, broadly disclose a pressure transducer with or without a switching mechanism but do not specifically disclose the desirable features in the fluid pressure transducer with a switching device, as described hereinafter.
The present invention incorporates desirable design features into the cylinder and piston of a mini oil pressure transducer. Specifically, the cylinder is made of a metal material interiorly, and a plastic material exteriorly. Grooves are formed into the metal cylinder inside walls to allow for engagement of bosses formed on the piston to prevent rotation of the piston as it moves within the cylinder. The plastic exterior configuration of the cylinder may be molded into a hexagon shape to provide wrenching flats for easier installation and removal of the unit. The perimeter portion of the grooves formed in the metal part of the cylinder also assist in preventing rotation of the plastic external part of the cylinder with respect to the metal internal part of the cylinder. The metal portion of the cylinder provides an electrical ground path to the base of a connector end. This is more economical to construct than insert molding the ground strap in the housing wall as previously done.
Therefore, an object of the invention described and claimed in this application is to provide a simple, compact, inexpensive yet reliable fluid pressure responsive transducer having operative parts and assemblies which are conveniently assembled together and therefore, easily serviced and that are associated together in a manner which prohibits rotation of the piston within the cylinder and of the interior metal portion of the cylinder within the exterior plastic portion of the cylinder. The foregoing and other objects and advantages will become more apparent when viewed in light of the accompanying drawings and following detailed description.